1st. You must rename layer of txd for used texture on dff (not txd file name). I'm check Zanoza Modeller (2.2.4) and now I know, that layer name must be "info2" instead of "png" (Import -> info.dff, in the bottom was name of setted texture layer).
2nd. You must compressed layer (DXT3 for Aplha) (4mb -> 1mb)
3rd. For integrate new objects with SAMP you must add collision to model.